In the context of this disclosure metal hydrides are elements and alloys or intermetallic compounds of elements that are capable of reversibly absorbing hydrogen. As used herein, the terms metal hydride and metal hydride alloy refer to both metal alloys in a non-hydrided state, sometimes referred to as metal hydriding alloys, and also to metal alloys in a hydrided state, which include the metal alloys with hydrogen. These metal hydride alloys may take shape as solid solution alloys or as intermetallic compounds. The hydrogen is incorporated within a matrix of metal atoms for storage in solid conditions. The matrix may comprise a lattice of a metal crystal structure, and the hydrogen atoms become interspersed between the metal atoms.
Metal hydride alloys are useful, for example, for the storage of hydrogen for fuel cells and other hydrogen-consuming power plants for automotive vehicles. Hydrogen may be absorbed in a non-hydrided metal composition (metal hydride precursor) by cooling the precursor material to a suitable, relatively cold, storage temperature and contacting it with hydrogen gas under a suitable, usually relatively high pressure. The hydrided metal hydride material is stored (often on a vehicle) until hydrogen is required. The metal hydride is then heated and hydrogen is released into a delivery system for providing hydrogen to a device (often an on-board device) that utilizes it.
Examples of combinations of metal(s) and corresponding hydrides include Pd and PdH0.6, LaNi5 and LaNi5H7, ZrV2 and ZrV2H5.5, FeTi and FeTiH2, and Mg2Ni and Mg2NiH4.
In practice, many metal hydride precursors may not readily absorb and store hydrogen. The particles require a pre-treatment before they take up hydrogen. The pretreatment (sometimes called “activation”) involves removing oxide films (or other hydrogen impermeable films) on the metal particles or fracturing some of the particles to expose un-oxidized surfaces for absorption of hydrogen. Such practices have included cooling the particles, pressurizing with hydrogen, heating, and depressurizing the particles to chemically remove oxide barriers to hydrogen absorption. Repeated cycling has sometimes been required.
There is a need for a less costly and time consuming practice for activation of hydrogen storage materials.